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One-Dose Covid-19 Vaccine Shown to Prevent Hospitalization

Syringe in hand

(Sam Moqadam, Unsplash)

3 Feb. 2021. Results from four international clinical trials show high disease prevention rates from one dose of the Oxford-AstraZeneca Covid-19 vaccine. Findings from the trials of the ChAdOx1 nCoV-19 vaccine in the U.K., South Africa, and Brazil are presented today in a non-peer reviewed preprint on The Lancet web site.

The analysis pools results from 17,177 participants, age 18 and over, in late-state clinical trials of ChAdOx1 nCoV-19 in the U.K. and Brazil, with early- and mid-stage trials in the U.K. and South Africa. Participants were randomly assigned to receive one dose ChAdOx1 nCoV-19 or a placebo, with a sub-group of the sample receiving a second dose of the vaccine 6 to 12 weeks later. Likewise, a subset of the two-dose sample received a lower dose of the vaccine in the first injection.

The study team, led by immunologist Andrew Pollard of the Oxford Vaccine Group, is looking primarily for cases of symptomatic Covid-19 cases in the samples, confirmed by standard diagnostics for SARS-CoV-2 viruses such as RT-PCR, as well reports of serious adverse effects from the vaccine. In addition, researchers are tracking hospitalizations, deaths, and immune system responses to the vaccine, as well as immediate adverse reactions to the vaccine. The team cut-off data collection in early December 2020, thus no results are reported on the recently discovered SARS-CoV-2 variants.

The findings show:

High rates of efficacy, 76 percent, defined as protection from symptomatic Covid-19 disease, from one dose of ChAdOx1 nCoV-19, measured after 21 days, that continued for another three months.

Efficacy rates for two-dose vaccine recipients ranged from 81 percent among those receiving the first low-dose injection to 63 percent for recipients of the standard dose both times, with higher efficacy rates when the second dose is given 12 weeks (82%) than six weeks later (55%).

No cases of Covid-19 disease severe enough for hospitalization in any vaccine recipients after 21 days, compared to 15 cases in placebo recipients, although two vaccine recipients were hospitalized before the vaccine could take effect.

Two-dose recipients maintained more of their neutralizing antibodies produced by ChAdOx1 nCoV-19 when the second dose was given 12 weeks after the first dose than six weeks later.

Vaccine recipients experienced lower infection rates by two-thirds (67%) after a single dose, and by half (50%) after two doses, which suggests less chance to spread the disease to others.

Vaccine formula derived from chimpanzee adenovirus

“This primary analysis reconfirms that our vaccine prevents severe disease and keeps people out of hospital,” says Menelas Pangalos, AstraZeneca’s executive vice president in a company statement. “In addition, extending the dosing interval not only boosts the vaccine’s efficacy, but also enables more people to be vaccinated upfront.”

The vaccine, code-named AZD1222 by AstraZeneca, is based on a technology developed at University of Oxford in the U.K. That technology, called ChAdOx1, uses a formula derived from an adenovirus in chimpanzees, similar to a virus in humans considered benign, or responsible at most for symptoms like the common cold.

In this case, the adenovirus is genetically engineered to keep from replicating in humans, with genetic material added to make proteins similar to the characteristic spike glycoprotein on the surface of SARS-CoV-2 viruses. That spike protein binds to receptors in human cells, to gain entry and cause Covid-19 infections.

As reported by Science & Enterprise in September 2020, AstraZeneca has a late-stage trial underway in the U.S., enrolling 30,000 U.S. adults at 62 sites. Participants are enrolling healthy individuals, but still at risk of infection from SARS-CoV-2 viruses, randomly assigned to receive two doses of the vaccine.

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